1. Field
An apparatus and a method that drives an LCD device are provided.
2. Related Art
Generally, liquid crystal display (LCD) devices adjust light transmittance of liquid crystal cells to display images, according to video signals. An LCD device of an active matrix type with switching elements that are formed in each liquid crystal cell, are widely used to display images thereon. The active matrix type LCD device mainly employs thin film transistors (TFT) as the switching elements.
FIG. 1 illustrates a schematic block diagram of an apparatus that drives an LCD device according to the related art.
Referring to FIG. 1, the related art LCD driving apparatus includes an image display unit 2 that includes liquid crystal cells that are formed at respective areas defined by n-th gate lines GL1 to GLn and m-th data lines DL1 to DLm. A data driver 4 provides analog video signals to the data lines DL1 to DLm. A gate driver 6 provides scan pulses to the gate lines GL1 to GLn. A timing controller 8 arranges data RGB inputted from the outside and provides it to the data driver 4 to generate data control signals DCS to control the data driver 4 and generate gate control signals GCS that control the gate driver 6.
The image display unit 2 includes a transistor array substrate and a color filter array substrate, which are bound with each other in a state where they face one another. Spacers are located between two array substrates to maintain the cell gap therebetween. The liquid crystal is filled in the space formed by the spacers between the two array substrates.
The image display unit 2 includes TFTs that are formed in areas that are defined by n-th gate liens GL1 to GLn and m-th data lines DL1 to DLm, and the liquid crystal cells connected to the TFTs. The TFTs respond to scan pulses from the gate lines GL1 to GLn and provide analog video signals from the data lines DL1 to DLm to the liquid crystal cells. The liquid crystal cells are composed of a common electrode and pixel electrodes connected to the TFTs, in which the common electrode and the pixel electrode face one another with respect to a liquid crystal layer. Therefore, the liquid crystal cells can be described as a liquid crystal capacitor Clc in an equivalent circuit. Such a liquid crystal cell includes a storage capacitor Cst that is connected to a previous stage gate line in order to maintain an analog video signal that is charged in a liquid crystal capacitor Clc until the next analog video signals are charged therein.
The timing controller 8 arranges the data RGB inputted from the outside to comply with the driver of the image display unit 2 and then provides it to the data driver 4. The timing controller 8 generates a data control signal DCS and a gate control signal GCS, using a dot clock DCLK, a data enable signal DE, and horizontal and vertical synchronous signals Hsync and Vsync. The data control signal DCS and a gate control signal GCS are used to control driving timings of the data driver 4 and the gate driver 6, respectively.
The gate driver 6 includes shift registers that sequentially generate scan pulses, or gate high pulses, in response to a gate start pulse GSP and a gate shift clock GSC in the gate control signal GCS from the timing controller 8. Such a gate driver 6 sequentially provides gate high pulses to the gate lines GL of the image display 2 to turn on the TFTs connected to the gate lines GL.
The data driver 4 converts an arranged data signal Data to an analog video signal. The arranged data signal Data is outputted from the timing controller 8 according to the data control signal DCS that is provided from the timing controller 8. The data driver 4 provides analog video signals that correspond to one horizontal line to the data lines DL each time a scan pulse is provided thereto, or each one horizontal period. The data driver 4 selects a gamma voltage that has a certain level according to gray levels of the data signal Data, and then provides the selected gamma voltage to the data lines DL1 to DLm. The data driver 4 reverses the polarity of the analog video signal, which is provided to the data lines DL in response to a polarity control signal POL.
The related art LCD driving apparatus's response speed is slow because of characteristics such as inherent viscosity and elasticity of liquid crystal. Although the liquid crystal response speed depends on, for example, physical properties of liquid crystal material and a cell gap, generally, the rising time of liquid crystal is 20˜80 ms and falling time of liquid crystal is 20˜30 ms. Because this response speed is longer than one frame period (16.67 ms in National Television Standards Committee (NTSC)) of a moving image, as shown in FIG. 2, the response of the liquid crystal proceeds to the next frame before a voltage being charged on the liquid crystal cell reaches a desired level.
Since a present frame for images, which are presently displayed on the image display unit, affects a next frame, a motion blurring phenomenon appears on the images displayed on the image display unit, as shown in FIG. 3. The motion blurring phenomenon means that moving images are blurry when displayed on the image display unit according to perception characteristics of viewers.
Therefore, the related art LCD driving apparatus and method have a decreased contrast ratio and thus image quality deteriorates, due to a motion blurring phenomenon generated in the displayed images.
In order to prevent such a motion blurring phenomenon in the relate art LCD device, an over-driving apparatus, which can modulate data signals for enhancing a liquid crystal response speed, is proposed.
FIG. 4 illustrates a block diagram of an over-driving apparatus according to the related art.
Referring to FIG. 4, the related art over-driving apparatus 50 includes a frame memory that stores data RGB of an inputted present frame Fn, a look up table that compares the data RGB of the inputted present frame Fn with data of a previous frame Fn−1 stored in the frame memory and that generates modulated data for enhancing liquid crystal response speed, and a mixer that mixes the modulated data from the look up table with the data RGB of the present frame Fn to output the mixing result thereto.
The look up table 54 records modulated data to be converted to a voltage greater than that of the data RGB of the present frame Fn in order to enhance the liquid crystal response speed, in which the voltage corresponds to a gray level of rapidly changed images.
Since the related art over-driving apparatus applies a voltage greater than that of a real data to a liquid crystal layer, using the look up table, as shown in FIG. 5, the liquid crystal in the liquid crystal layer can rapidly respond to comply with an objective gray level voltage. When the voltage reaches to the actual desired gray level, the gray level is maintained.
The related art over-driving apparatus enhances the liquid crystal response speed using a modulated data R′G′B′, such that a motion blurring phenomenon of displayed images can be reduced.
When the related art LCD device displays images using the over-driving apparatus, the displayed images are not clear due to a motion blurring phenomenon which occurs at the boundary parts A and B of each displayed image, as shown in FIG. 6. In other words, since luminance increases between the boundaries A and B of the image to have a tilt, motion blurring still occurs even though the liquid crystal is driven at high speed.